Inkjet printing mechanisms may be used in a variety of different products, such as plotters, facsimile machines and inkjet printers, to print images using a colorant, referred to generally herein as “ink”. These inkjet printing mechanisms use inkjet cartridges, often called “pens”, to shoot drops of ink onto a page or sheet of print media.
Each pen has a printhead formed with very small nozzles through which the ink drops are fired. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, Hewlett-Packard Company. In a thermal system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor.
By selectively energizing the resistors as the printhead moves across the sheet, the ink is expelled in the desired locations on the print media. The nozzles are typically arranged in one or more linear arrays. If more than one, the two linear arrays are generally located side-by-side on the printhead, parallel to one another, and perpendicular to the scanning direction. Thus, the length of the nozzle arrays defines a print swath or band. That is, if all of the nozzles of one array are continually fired as the printhead makes one complete traverse through the printzone, a band or swath of ink would appear on the sheet. The height of this band is known as the “swath height” of the pen, the maximum pattern of ink that can be laid down in a single pass.
To print an image, (e.g., picture, chart or text) the print media is moved relative to the printhead after a swath has been printed, so that a further swath may be printed adjacent to the earlier swath. By a repetition of this process, a complete printed page may be produced in an incremental manner.
To clean and protect each printhead in order to ensure satisfactory print quality, a “service station” mechanism is typically located within the printer chassis so the printhead can periodically be moved over the station for maintenance.
Generally, such service stations include a number of elastomeric wipers, used to wipe the printhead surface with an ink solvent, such as a polyethylene glycol (“PEG”) compound to remove ink residue, as well as any paper dust or other debris that has collected on the-face of the printhead. Service stations usually include a capping system that seals and protects the printhead nozzles from contaminants and drying during non-printing periods, or during storage. Some caps are also designed to facilitate priming, such as by being connected to a pumping unit or other mechanism that draws a vacuum on the printhead. Additionally, service stations usually include one or more reservoirs, termed “spittoons” which are designed to receive and store drops of ink ejected during “spitting” operations. “Spitting” is the term given to the process by which a number of ink drops are fired through one or more nozzles of a printhead in order to unblock a nozzle that may be clogged by dried ink or other matter.
In known spittoon designs two problems are known to arise. The first of these is caused by the generation of airborne aerosol droplets of ink when spitting operations are performed. Such aerosol droplets can cause many problems in printers. For example, airborne droplets may visibly stain areas of the printer with which they come into contact. These areas may include optical devices and sensors used in the printer, thus reducing their effectiveness. Additionally, however, if the aerosol ink of one color ink comes into contact with the pen of a different color ink, or indeed the servicing equipment associated with a pen of a different color ink, cross contamination of the ink may arise. This may lead to a visible deterioration in the quality of the printed output of the printer, which may even require the replacement of an effected pen and its associated servicing equipment.
The amount of aerosol ink that is generated during a spitting operation is dependent upon a variety of factors. These may include: the architecture of the pens; the firing frequency; the ink drop volume; the composition of the ink; and, the temperature. However, it is also dependent upon the design of the spittoon used together with the “spitting distance”; i.e. the distance that the ink drops travel between leaving the printhead and contacting a surface of the spittoon or liquid ink held in the spittoon. In general, there exists a desirable spitting distance, beyond which the greater the spitting distance the greater the amount of aerosol that will be generated.
The second problem associated with spittoon designs concerns space. With many printers for example, especially those intended to be located upon a desk top, it is generally desirable that their size (especially their “footprint”) should be as small as possible. Since printer service stations are generally laterally offset from the printzone, their size often contributes directly to the footprint of the printer. Thus, there is an incentive to reduce the size of the service stations and spittoons as far as possible.
Because of the space restrictions imposed upon the design of printer service stations, a trade off usually exists between the size of the printer and both the design of the spittoon and the spitting distance; both of which effect the amount of aerosol droplets generated when spitting operations are performed.
It would therefore be desirable to provide a system for servicing ink jet pens, which overcomes one or more of the above problems.